P.-S. Kuo

Stress-Induced Hump Effects of p-Channel Polycrystalline Silicon Thin-Film Transistors

Positive bias temperature instability in p-channel polycrystalline silicon thin-film transistors is investigated. The stress-induced hump in the subthreshold region is observed and is attributed to the edge transistor along the channel width direction. The electric field at the corner is higher than that at the channel due to thinner gate insulator and larger electric flux density at the corner. The current of edge transistor is independent of the channel width. The electron trapping in the gate insulator via the Fowler-Nordheim tunneling yields the positive voltage shift. As compared to the channel transistor, more trapped electrons at the edge lead to more positive voltage shift and create the hump. The hump is less significant at high temperature due to the thermal excitation of trapped elections via the Frenkel-Poole emission.

A high efficient 820 nm MOS Ge quantum dot photodetector

A Ge quantum dot photodetector has been demonstrated using a metal-oxide-semiconductor (MOS) tunneling structure. The oxide film was grown by liquid phase deposition (LPD) at 50/spl deg/C. The photodetector with five-period Ge quantum dot has responsivity of 130, 0.16, and 0.08 mA/W at wavelengths of 820 nm, 1300 nm, and 1550 nm, respectively. The device with 20-period Ge quantum dot shows responsivity of 600 mA/W at the wavelength of 850 nm. The room temperature dark current density is as low as 0.06 mA/cm/sup 2/. The high performance of the photodetectors at 820 nm makes it feasible to integrate electrooptical devices into Si chips for short-range optical communication.

Strained Pt Schottky diodes on n-type Si and Ge

In summary, the reduction of the Schottky-barrier height for the n-type semiconductor under external mechanical strain is observed. This reduction is shown to originate from the reduction of conduction band edge. The boundary condition under uniaxial strain technology is stress-free along the direction perpendicular to uniaxial stress obtain the reasonable agreement between data and theoretical calculation

Novel MIS Ge-Si quantum-dot infrared photodetectors

The metal-insulator-semiconductor (MIS) Ge-Si quantum-dot infrared photodetectors (QDIPs) are successfully demonstrated. Using oxynitride as gate dielectric instead of oxide, the operating temperature reaches 140 and 200 K for 3-10 and 2-3 /spl mu/m detection, respectively. From the photoluminescence spectrum, the quantum-dot structures are responsible for the 2-3 /spl mu/m response with high operation temperature, and the wetting layer structures may be responsible for the 3-10 /spl mu/m response. This novel MIS Ge-Si QDIP can increase the functionality of Si chip such as noncontact temperature sensing and is compatible with ultra-large scale integration technology.

Hole mobility enhancement of Si0.2Ge0.8 quantum well channel on Si

The ultrathin strained Si0.2Ge0.8 quantum well channel (∼5nm) directly grown on Si substrates is demonstrated with low defect density and high hole mobility. The quantum well Si0.2Ge0.8 channel reveals an ∼3.2 times hole current enhancement and an ∼3 times hole mobility enhancement as compared with the bulk Si channel. The output current-voltage characteristics under the external mechanical strain confirm the compressive strain in the channel. The external compressive strain further enhances the hole mobility in a Si0.2Ge0.8 channel.

Recessed Oxynitride Dots on Self-Assembled Ge Quantum Dots Grown by LPD

Recessed oxynitride dots deposited on self-assembled Ge dots are demonstrated using liquid-phase deposition (LPD). By adding ammonia into the solution, the nitrogen atoms can be incorporated into the deposited film. The tensile strain of the Si cap layer directly deposited on Ge dots can enhance the oxynitride nucleation and deposition on Si surface. The tensile strain may also increase the etching rate of the Si cap layer and the recessed dots are formed directly above the Ge dots. The LPD-SiON dots have a higher dot step height as compared to LPD-SiO 2 dots.

Electrically pumped Ge Laser at room temperature

The stimulated emission from (110) Ge was observed in the metal-insulator-semiconductor (MIS) laser diode with a simple Fabry-Perot cavity by current injection at room temperature. The lasing characteristics consist of (1) sudden increase of efficiency in the light-out current-in curve, (2) the transverse electrical mode polarization, (3) the strong directivity of the far field pattern, (4) the narrow line width in the emission spectra above the threshold, and (5) the population inversion confirmed by fitting the spontaneous emission spectrum near the threshold current. The lasing wavelength is suitable for Si photonics due to the emission energy lower the Si bandgap.

Dynamic bias temperature instability of p-channel polycrystalline silicon thin-film transistors

The impact ionization that occurred near channel-S/D junctions is responsible for the dynamic bias temperature instability (BTI) of p-channel poly-Si thin-film transistors (TFTs). Impact ionization is induced by lateral electric field when gate voltage switches from inversion or full-depletion to accumulation bias. Drain current increases initially due to shortened effective channel length. As the stress time increases, the grain barrier height increases to reduce the drain current, especially at high temperature. In addition to the transient switches, the plateau portions of the gate pulse have significant impact on the device degradation for large stress amplitudes.

Electroluminescence from monocrystalline silicon solar cell

The band edge emission with the peak at 1.15 μm is observed at room temperature from monocrystalline silicon solar cell at forward bias. The electroluminescence spectra can be fitted by electron hole plasma recombination model. The temporal response of electroluminescence is used to characterize the minority carrier lifetime by fitting the time evolution of radiative recombination using the Shockley–Read–Hall, radiative, and Auger recombination models. The minority carrier lifetime is almost constant (1.8 ms) for excess carrier density lower than 4×1015 cm−3, and then decreases at higher concentration.

Narrow-band metal-oxide-semiconductor photodetector

Si-based photodetectors for narrow-band ultraviolet light (319 nm) and green light (500 nm) detection are demonstrated using a metal-oxide-semiconductor tunneling structure. By using appropriate selection of gate metal, the metal-oxide-semiconductor tunneling diode can detect specific range of light. Due to the spectral dependence of absorption and reflection of the Ag and Au as gate electrodes, the narrow-band detection of ultraviolet and green light can be achieved, respectively. The photodetectors with 130 nm thick Ag gate and 70 nm thick Au gate exhibit peak responsivities of 5.1 and 0.3 mA/W at 319 and 500 nm, respectively.